Differential hydraulic servomotor



Aug. 31, 1954 A. P. GLENNY ETAL DIFFERENTIAL HYDRAULIC SERVOMOTOR Filed April 11, 1950 7026205 MOTOR Inventors P. 611.: MW. zmws L. SPENcCR.

Patented Aug. 31, 1954 2,687,706 DIFFERENTIAL HYDRAULIC SERVOMOTOR Arthur Philip Glenny, Castle Way, Hanworth, and Dennis Lincoln Spencer, West Twyford, London, England, assignors to The Sperry Gyroscope Company Limited, Brcntford, Eng land, a company of Great Britain Application April 11, 1950, SeriallNo. 155,234

Claims priority, application Great Britain April 11, 1949 Claims. (01. 12138) The pr nt ention relates to hydraulic ends of the cylinder which path opens autoservo-system o p ng a Working cylinder and matically on a fall in pressure in the small end.

is attached to one face thereof to provide unequal opens when the pressure 1n the system falls as a opposed Working areas. result of the main supply valve being closed.

Such a system as that outlined above can be The valve may take the form of a spring-loaded made to operate automatically in response to sigball located in the piston head and controlling instance by a controlled mechanism, andin an formed in the piston and piston-rod. Alterautomatic servo-system of this nature it is often natively it may be a piston-ring located in a desired to change from automatic to what may groove in the piston in such a manner that on rise be referred to as manual control. In order to do of pressure in the system the ring moves to seal this, it is necessary to shut off the supply preson communicating ports between the two faces provide a valve, other than a main supply valve, age path by way of the said ports.

to connect both ends of the cylinder to waste: it In order that the invention may be more readily is not suflicient merely to interconnect the two understood, reference will now be made to the acends because subsequent manual movement companying drawing which shows a schematic area thereof, displaces more liquid than can be of, which i given by way of example only.

if the larger end is not opened to Waste, the servo liquid supply lines, one shown at 2, to the large end is hydraulically locked. I and another, shown at 3, to the small end of the It is the particular object of the present invencylinder. A piston d and piston-rod 5 are artion to ensure that removal of the supply presranged to be translated in the cylinder by pressure manual control, regardless of the position of the the medium of the pressure-liquid introduced automatic control valve, and without hydraulic through the supply lines. The area of the piston lock.

but in which it may be necessary to assume direct 40 anced Whenever the pressure on the small end is system, that is, from hydraulic lock. that a constant pressure is applied to the small Hereinafter, we shall refer to the end of the end and varying pressures are applied to the large cylinder through which the piston rod passes as 5 end through control means to obtain automatic the small end and the other end as the large operation of the system.

end. The two supply lines 2 and 3 are connected According to the invention, a system such as to asource of main supply of pressure-liquid conhas hitherto been referred to, is characterised trolled by a main supply valve 6 and in the line by the provision of a waste valve in the supply from the large end there is provided a balanced line to the small end of the cylind r, which valve valve 1 which is operated by a torque motor a sure is cut of? to connect the small end to waste, ergised, for example, by signals from an automatic so that the pressure therein falls, and by the procontrol system such as an automatic pilot for vision of a variable leakage path between the two ships or aircrafawhich is not shown Increasing signals to the torque motor 8 are caused to move the balanced valve 1 against the spring bias 9 in such a manner as to admit pressure-liquid to the large end of the cylinder through the line 2 and if this be the upper end, as shown, then the piston 4 is forced down. Decreasing signals to the torque motor 8 cause the valve 1 to move in the opposite direction under the influence of the spring and open the large end to waste via line 2.

In the supply line 3 to the small end, there is provided a waste valve it in the form of a springloaded ball-valve so loaded as to tend to open it to waste when the pressure drops, that is to say, when the main supply valve 6 is closed, the small normal leakage causes the pressure to drop in the system and valve lfl' thereupon opens the small end of the piston to waste.

To engage automatic control, the main supply valve 6 is opened and thus pressure-liquid is supplied to the small end of the cylinder, escaping from the waste valve l until the pressure drop and velocity past the ball-valve is sufficient to close the valve against the spring, after which the pressure-rise maintains it closed. As an example, with a main supply pressure of 1,000 lbs/sq. in., the waste valve In might be arranged to close at 200 lbs/sq. in.

The piston 4 is provided with a leakage-valve comprising, in this embodiment, a spring-loaded ball ll similar to the waste valve IE1, arranged in the piston and controlling the flow of pressureliquid in a passage l2, I3 formed in the piston head and adjacent portion of the piston-rod respectively and communicating through small passage 28 with that part of the cylinder that surrounds the piston-rod, i. e. the small end of the cylinder, in effect providing a leakage between the small and large ends thereof.

In the system described, a constant high unit pressure is supplied at the small end of the piston, while the unit pressure at the large end of the piston is normally about one half of the pressure at the small end, the servo control being effected by varying the pressure at the small end above and below the aforesaid mean half pressure by the balanced control valve 1 under the influence of the movement imparted thereto by the torque motor 8. When under automatic control, the uniform high pressure at the low end of the piston keeps the valve H closed because when the ball is seated on its seat formed at the end of the pipe 20, the efiective area of the ball ll exposed to the high pressure in passage i2 is greater than the effective area of the ball which is exposed to the pressure at the large side of the piston. This is because the diameter of the first mentioned area is that of the external diameter of the pipe 26, while the diameter of the second mentioned area is equal to the internal diameter of the pipe. Preferably, the ball and the pipe or tube are lapped together to form a seat at the end of the pipe.

To operate under manual control, the main supply valve 6 is closed and the resultant fall in pressure in the system due to normal leakage as the valve remains closed allows the spring biased waste valve iii and the spring biased piston leakage-valve H to open, thereby opening to waste the oil on both sides of the piston Ad. This means that there is a leakage path for pressure liquid past the piston and to waste so that manual control is easily effected.

It is obvious that instead of a by-pass valve i l and passage 20 in the piston head, other by-pass means may be provided within the scope of this invention as long as a leakage path past the piston is provided so that the servo may be operated manually without undue restraint.

It will be understood that the invention has only been described by way of example and that various modifications may be made to the specific details set forth above, without in any way departing from the scope thereof.

What is claimed is:

1. An hydraulic servo-system comprising a working cylinder, a piston slidably positioned within the cylinder, a piston rod secured on one side of the piston and extending out one end of the cylinder in sealed relation thereto, said rod reducing the piston area to substantially one half the area of the opposite side of the piston, a highpressure hydraulic fluid source, a first hydraulic line connecting said source to the cylinder adjacent the piston rod end thereof, a second hydraulic line connecting said source to the opposite end of the cylinder, a spring-loaded check valve in said first line adapted to open the line to waste when the pressure drops substantially, a balanced valve in the second line, a torque motor secured to the valve for moving it in one direction, a bias spring secured to the valve to move the valve against the torque of the motor, said bias spring moving the valve to open said second line to waste and said motor moving the valve to open said second line to the fluid source, a biased pressureoperated valve in the piston adapted to close when the pressure in the first line exceeds the pressure in the second line, and a main valve connected between the source and the two lines for cutting off the hydraulic fluid, whereby the check valve opens as the pressure drops, thus permitting manual movement of the piston.

2. An hydraulic servo-system comprising a working cylinder, a piston slidably positioned within the cylinder, a piston rod secured to one side of the piston and extending out one end of the cylinder in sealed relation thereto, a high pressure hydraulic fluid source, a first hydraulic line connecting said source to the cylinder adjacent the piston-rod end thereof, a second hydraulic line connecting said source to the opposite end of the cylinder, a spring-loaded check valve in said first line adapted to open the line to waste when the pressure drops substantially, a balanced valve in the second line for connecting the second line either to the source or to waste, a pressureoperated valve in the piston adapted to close when the pressure in the first line exceeds the pressure in the second line, and a main valve connected between the source and the two lines for cutting off the hydraulic fluid, whereby the check valve opens as the pressure drops, thus permitting manual movement of the piston.

3. An hydraulic servo-system comprising a working cylinder, a piston slidably mounted within the cylinder, and having one face thereof of substantially greater effective area than the opposite face, a high-pressure hydraulic fluid source, a first hydraulic line connecting said source to the cylinder adjacent the smaller piston face, a second hydraulic line controllably connecting said source to the opposite end of the cylinder, a valve means in said first line adapted to open the line to waste when the pressure drops substantially, a controlled valve in the second line for connecting the second line either to the source or waste, a valve means in the piston adapted to close when the pressure in the first line .exceeds the pressure in the second line and to mit free movement of the piston.

5. A hydraulic servo control system of the kind in which the hydraulic motor has a working cylinder and a piston having opposing faces of difierent areas and ntrolled the small e ge interconnecting the large and nds of the cylinder, a by-pass valve References Cited in the file of this patent Number Number UNITED STATES PATENTS 

